1. Field of the Invention
This invention relates to a gas discharge panel drive system, and more particularly to a drive system for an alternating AC current driven type gas discharge panel which is capable of high resolution display.
2. Description of the Prior Art
A gas discharge panel, in which electrodes covered with dielectric layers are disposed opposite to each other across a space having sealed therein a discharge gas, is known under the name of a plasma display panel. In such a gas discharge panel heretofore employed, X-direction electrodes (hereinafter referred to as X electrodes) xi (i = 1, 2, 3, . . .) and Y-direction electrodes (hereinafter referred to as the Y electrodes) yj (J = 1, 2, 3, . . .) are disposed to intersect each other at right angles, and electrode pitches px and py are equal to each other, as shown, for example, in FIG. 1, which is a diagrammatic representation of the electrode arrangement in a conventional or "prior art" gas discharge panel. A sustain pulse is applied to each electrode and, in the case of a write operation, a write pulse is applied to each of selected ones of the X and Y electrodes. Letting a firing voltage and a minimum sustain pulse voltage (of a discharge point C.sub.ij at the intersection of the electrodes xi and yj) be represented with V.sub.f and V.sub.sm, respectively, a pulse voltage V.sub.s is selected to bear a relationship, V.sub.sm &lt; V.sub.s &lt; V.sub.f, and a write pulse voltage V.sub.w to the selected discharge point is selected to have a relationship, V.sub.f &lt; V.sub.w.
FIG. 2 shows an example of a driving waveform. Reference characters V.sub.xa and V.sub.ya indicate voltages applied to selected ones of the X and Y electrodes, respectively; V.sub.xb and B.sub.yb designate voltages applied to unselected X and Y electrodes, respectively; V.sub.a identifies a voltage applid to a selected discharge point; PS denotes a sustain pulse of the voltage V.sub.s ; PWX represents a positive half selection write pulse of a voltage V.sub.xw ; PWY shows a negative half selection write pulse of a voltage V.sub.yw ; and PW refers to a write pulse of a voltage V.sub.xw + V.sub.yw = V.sub.w. For example, in the case of writing information in a discharge point C33 at the intersection of the electrodes x3 and y3 in the panel shown in FIG. 1, a pulse train identified by the waveform V.sub.xa and a pulse train indicated by the waveform V.sub.ya are applied to the electrodes x3 and y3, respectively, and pulse trains identified by waveforms V.sub.xb and V.sub.yb, respectively, are applied to the other unselected electrodes, by which the write pulse of the composite write pulse voltage V.sub.w = V.sub.xw + V.sub.yw is applied to the discharge point C33 at the timing of write. Since the write pulse voltage V.sub.w is higher than the firing voltage V.sub.f, a discharge spot is produced at the discharge point C33.
FIG. 3 is a graph showing the write characteristic of the conventional gas discharge panel described above, the ordinate representing the sustain pulse voltage V.sub.s and the abscissa representing the composite write pulse voltage V.sub.w, and the hatched range being a normal operation region. For example, where the sustain pulse voltage V.sub.s has a value V.sub.sl, the lowest composite write pulse voltage is V.sub.wl, above which write is possible. As the voltage V.sub.w gradually rises, the intensity of a write discharge due to a charge coupling effect increases, resulting in an erroneous discharge or misfire of the neighboring discharge points owing to half selection. The range in which such misfire is not caused is defined as the write operation margin, and the composite write pulse voltage V.sub.w must be set in such a range.
The present inventors have discovered polarity dependency of the write pulse in the phenomenon of causing such misfire at the neighboring discharge points. That is, when the composite write pulse voltage of the positive and negative write pulses PWX and PWY (FIG. 2) applied to the electrodes x3 and y3, respectively, is V.sub.whl, misfire is produced at the neighboring discharge points C32 and C34 along the electrode x3 supplied with the positive half selection write pulse PWX, but no misfire is caused at the neighboring discharge points C23 and C43 along the electrode y3 supplied with the negative half selection write pulse PWY, even if the voltages V.sub.xw and V.sub.yw of the half selection write pulses PWX and PWY, respectively, are equal to each other. When the composite write pulse voltage further increases to a value V.sub.wh2, misfire is also produced at the abovesaid discharge points C23 and C43. That is, the neighboring discharge points in the X- and Y-directions, in which misfire is caused by half selection, differ with the polarity of the write pulse.